Consider: if we can write the software that cities, states, and even the federal government uses to do it's job, then we can also have a material impact on transparency, usability, etc for the users.
Take the judicial system. It is badly underfunded, especially in California, which has the largest civil court system in the Western world. What if an enterprising group of civic minded programmers simply wrote awesome, free, open software to run a state courtroom, complete with a self-help web interface?
Such a project would not necessarily be fun. But it would be useful, and it would arguably contribute greatly to society.